Method and Apparatus for Rapid Preparation of Multiple Specimens for Transmission Electron Microscopy
A method and apparatus for in-situ lift-out rapid preparation of TEM samples. The invention uses adhesives and/or spring-loaded locking-clips in order to place multiple TEM-ready sample membranes on a single TEM support grid and eliminates the use of standard FIB-assisted metal deposition as a bonding scheme. Therefore, the invention circumvents the problem of sputtering from metal deposition steps and also increases overall productivity by allowing for multiple samples to be produced without opening the FIB/SEM vacuum chamber.
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This application claims one or more inventions which were disclosed in Provisional Application No. 61/413,083, filed Nov. 12, 2010, entitled “METHOD AND APPARATUS FOR RAPID PREPARATION OF MULTIPLE SPECIMENS FOR TRANSMISSION ELECTRON MICROSCOPY”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention is in the technical field of methods of sample preparation and manipulation for preparing a specimen for transmission electron microscopy (TEM) examination. More particularly, the present invention is in the technical field of sample preparation and manipulation by methods of in-situ lift-out techniques.
2. Description of Related Art
The standard in-situ lift-out method involves moving a micromanipulator probe to a sample membrane that was previously milled from a wafer by use of a focused ion beam/scanning electron microscope (FIB/SEM) or similar machine. This leaves the sample membrane approximately 1-2 microns thick with varying length and height (typically 5-15 micron length and 5-15 micron height). The micromanipulator probe is then welded to the sample membrane by ion beam assisted metal deposition. When the weld is secured, the sample membrane is then cut from the wafer by a focused ion beam (FIB) and extracted from the wafer.
The probe then moves the sample to a transmission electron microscope (TEM) grid where it is welded to the TEM grid by ion beam assisted metal deposition. When the sample membrane is secured to the TEM grid, the probe is cut from the sample by FIB. The sample membrane is then milled again by FIB until it is thin enough for use in a TEM, typically between 50-200 nanometers thick. The entire method is done within the FIB/SEM machine chamber while it is activated and under vacuum.
The current method of in-situ lift-out has a low productivity, as the number of samples that are produced is relatively low in comparison to the total amount of time and effort that is used for this purpose. Features that shorten the time of preparing a sample and/or increase user productivity are highly desirable in this field.
The current method also has problems in metal deposition steps where excess material may sputter on, and contaminate unintended objects.
SUMMARY OF THE INVENTIONThe present invention provides a method and apparatus for in-situ lift-out rapid preparation of samples for electron microscopy. The invention uses adhesives and/or spring-loaded locking-clips in order to place multiple sample membranes on a single support grid and eliminates the use of standard FIB-assisted metal deposition as a bonding scheme. Therefore, the invention circumvents the problem of sputtering from metal deposition steps and also increases overall productivity by allowing for multiple samples to be produced without opening the FIB/SEM vacuum chamber.
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- 101: Place wafer, microprobe assemblies and TEM support grid into FIB/SEM chamber—Set up all the necessary parts in order to do an in-situ lift-out according to the method shown in the flowchart 100. A wafer, microprobe assemblies, and TEM support grids are loaded into a FIB/SEM chamber, which is then activated, placing all its contents under vacuum.
- 102: Place microprobe assembly in micro gripping and manipulation device—a micro gripping and manipulation device reaches and grasps a micromanipulator probe, which has an adhesive or a spring loaded locking clip at the end of it.
- 103: Ion mill sample membrane from wafer—the FIB/SEM is used to create a sample membrane by etching out portions of the wafer using an ion beam. The sample membrane will be approximately 5-15 microns long, 5-15 microns deep, and less than 200 nanometers thick when the step is completed. The sample membrane will also be partially cut away from the wafer.
- 104: Attach microprobe assembly to sample membrane—the micro gripping and manipulation device moves the micromanipulator probe so that the adhesive or spring loaded locking clip will touch and attach to the sample membrane. The sample membrane is attached to both the wafer and the microprobe assembly.
- 105: Detach sample membrane from wafer—the sample membrane is completely severed from the wafer by the FIB/SEM ion beam. The sample membrane is now only attached to the microprobe assembly.
- 106: Move microprobe assembly with attached sample membrane to a TEM support grid—the microprobe assembly is moved from the wafer to the TEM support grid so that the sample membrane is over a hollow viewing window.
- 107: Secure microprobe assembly with attached sample membrane to a TEM support grid—the microprobe assembly is attached to the TEM support grid using an adhesive or a spring loaded locking clip so that it is secured to the TEM support grid.
- 108: Release microprobe assembly from micro gripping and manipulation device—the micro gripping and manipulation device releases the microprobe assembly with sample membrane only attached to the TEM support grid.
- 109: Repeat Process?—the process may be repeated to create and attach more sample membranes to the TEM support grid.
If yes, return to step 102 and repeat the method;
If no, go on to the last step.
- 110: Remove TEM support grid from FIB/SEM for examination—the TEM support grid has as many sample membranes attached to it as required by the user and the FIB/SEM is deactivated, releasing the vacuum chamber. The TEM support grid is removed so that it can by viewed by a TEM.
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The micromanipulator probe 22 may vary in size, length, or geometry, but must be usable with typical manipulating devices that are compatible with FIB/SEM machines. The spring loaded locking clip 23 is securely attached to the micromanipulator probe 22 and must apply sufficient force in order to latch and hold onto the sample membrane 24.
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The modified TEM slotted support grid 43 is a typical TEM slotted support grid used in the art. It is approximately 3 millimeters in diameter with a slotted hole in the middle. It is made of typical metals used in the art, such as copper, molybdenum or others. The TEM slotted support grid is modified by cutting a portion away from the grid so that the cut is roughly parallel with the long axis of the hollow slot. The extent of cut is variable, but leaves the hollow slot of the slotted TEM grid intact.
Referring now to 9-C, there is shown a micro gripping and manipulation device 50 near a micromanipulator probe 51 which is attached to a temporary bonding agent 52, which is attached to a modified TEM slotted support grid 53.
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The modified TEM slotted support grid 62 is a typical TEM support slotted grid used in the art or a close variation of it. It is typically approximately 3 millimeters in diameter with a slotted hole in the middle. It is made of typical metals used in the art, such as copper, molybdenum or others. The modified TEM slotted support grid 62 is modified by cutting a portion away from the grid so that it is roughly parallel with the long axis of the slot. The extent of cut is variable, but leaves the slotted portion of the support grid intact.
The advantages include, without limitation, that it allows for multiple sample membranes to be placed on a single TEM support grid for viewing by a TEM or similar machine. The method further avoids the need for assisted metal weld deposition and its inherent metal sputtering on and around the area of interest for microscopy. The method further allows for SEM only type of machines to continue the lift-out process, thereby freeing the more expensive FIB/SEM machine from the downtime of the in-situ lift-out attachment process.
While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention.
Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.
Claims
1. A method for in-situ lift-out preparation of samples for electron microscopy in a microscopy chamber having at least one viewing window, using a micro gripping and manipulation device and a microprobe assembly having an adhesive or a spring loaded locking clip at an end, the method comprising:
- a) placing a wafer, microprobe assemblies and a support grid into an electron microscopy chamber;
- b) placing the microscopy chamber under vacuum;
- c) grasping the microprobe assembly with the micro gripping and manipulation device;
- d) creating a sample membrane by etching out portions of the wafer using an ion beam;
- e) using the micro gripping and manipulation device to move the microprobe assembly so that the adhesive or spring loaded locking clip will touch and attach to the sample membrane;
- f) severing the sample membrane from the wafer;
- g) moving the microprobe assembly with the attached sample membrane to the support grid, so that the sample membrane is over a viewing window;
- i) securing the microprobe assembly to the support grid; and
- j) releasing the microprobe assembly from the micro gripping and manipulation device.
2. The method of claim 1, further comprising creating and attaching more sample membranes to the support grid by repeating the method from step c until all sample membranes have been created and attached.
3. The method of claim 1, further comprising the steps of:
- k) deactivating the microscopy chamber, releasing the vacuum; and
- l) removing the support grid.
4. The method of claim 1, wherein the sample membrane is etched in step d to a size in the range of 5-15 microns in length, 5-15 microns in depth and less than 200 nanometers in thickness.
5. The method of claim 1, in which step d further comprises partially cutting the sample membrane away from the wafer.
6. The method of claim 1, in which in the step f the sample membrane is completely severed from the wafer by the FIB/SEM ion beam.
7. The method of claim 1, in which in step i the microprobe assembly is secured to the TEM support grid using an adhesive or a spring loaded locking clip.
8. An apparatus for in-situ lift-out preparation of electron microscopy samples comprising:
- a) a micro gripping and manipulation device;
- b) a microprobe assembly having a first end for gripping by the micro gripping and manipulation device, and a second end; and
- c) an attachment element at the second end of the microprobe assembly.
9. The apparatus of claim 8, in which the attachment element is an adhesive.
10. The apparatus of claim 9, in which the adhesive is usable in a vacuum chamber environment.
11. The apparatus of claim 9, in which the adhesive is curable by exposure to charged electron particles.
12. The apparatus of claim 8, in which the attachment element is a spring loaded locking clip.
13. The apparatus of claim 12, in which the spring loaded locking clip is made of a metal pliable enough to exert a force suitable to hold a sample without inflicting damage to the sample.
14. The apparatus of claim 8, in which the microprobe assembly is made of metal.
15. The apparatus of claim 14, in which the metal is tungsten.
16. The apparatus of claim 14, in which the metal is molybdenum.
17. The apparatus of claim 8, in which the micromanipulator probe is cylindrical and tapers from the first end to a point at the second end.
18. The apparatus of claim 8, further comprising a mesh support grid for supporting a plurality of micromanipulator probes attached to samples.
19. The apparatus of claim 18, in which the mesh support grid further comprises a curable grid adhesive for adhering the micromanipulator probe to the mesh support grid.
20. The apparatus of claim 18, in which the mesh support grid further comprises a slotted support grid.
21. The apparatus of claim 20, in which the slotted support grid has a temporary bonding agent for removably bonding the micromanipulator probe to the slotted support grid.
22. The apparatus of claim 20, in which the micromanipulator probe has a temporary bonding agent for removably bonding the micromanipulator probe to the slotted support grid.
23. The apparatus of claim 18, in which the mesh support grid further comprises a plurality of viewing windows.
24. The apparatus of claim 18, in which the mesh support grid is made of metal.
25. The apparatus of claim 24, in which the metal is copper.
26. The apparatus of claim 24, in which the metal is molybdenum.
27. The apparatus of claim 18, in which the mesh support grid is approximately 20-50 microns thick.
28. The apparatus of claim 18, in which the mesh support grid is circular or semicircular.
29. The apparatus of claim 28, in which the mesh support grid has a diameter of approximately 3 millimeters.
Type: Application
Filed: Mar 17, 2011
Publication Date: May 17, 2012
Patent Grant number: 8258473
Applicant: NANOTEM, INC. (Scottsdale, AZ)
Inventors: Frederick F. Shaapur (Scottsdale, AZ), Roger J. Graham (Scottsdale, AZ)
Application Number: 13/050,561
International Classification: G21K 5/08 (20060101); G01N 23/00 (20060101);